The ability to manipulate and move droplets on a surface in a non-contact, controllable manner could enable numerous applications, such as lab-on-a-chip devices, where programmable droplet motion is desired without requiring bulky instruments. To this end, studies have investigated driving forces to manipulate water droplets, such as electrocapillary forces in electrowetting-on-dielectric (EWOD), and thermal, chemical, and/or surface morphological gradient forces. While exploitation of these driving forces shows promise, the manipulation of droplets on surfaces remains challenging due to contact angle hysteresis (CAH) of water droplets. In order to move a droplet on a surface, the driving force(s) need to overcome the opposing force caused by CAH, which may be prohibitively high.
Shape memory polymers (SMPs) encompass a broad range of responsive polymers that can retain a configurational “memory” of an initial or permanent shape that can be recovered from a deformed or temporary shape upon exposure to a suitable stimulus. In the case of a thermo-responsive SMP, heating the polymer at or beyond its glass transition temperature (Tg) induces a drastic transition in elastic modulus from the “glassy” or rigid state to the rubbery state. As a consequence of this unique memory capability, SMPs have been extensively studied and exploited for many applications, including robotics, biomedical devices, microassembly, dry adhesives, and sensors.